The present disclosure relates to a variable valve drive for a lifting valve, in particular for a charge exchange valve of an internal combustion engine, which is periodically movable between a closed position and an open position indirectly by a cam via a rocker lever.
It is known for gas exchange valves of an internal combustion engine to be operated in a variable manner with different opening and closing times and with different valve opening lifts. Such variable valve drives offer the advantageous possibility of targeted adaptation of the profile of the valve lift curve over the cam angle as a function of operating parameters of the device that is equipped with the respective lifting valve, that is to say for example as a function of rotational speed, load or temperature of an internal combustion engine.
In particular, it is known for multiple different lift curves for a lift valve to be generated by virtue of multiple cams being provided for the actuation of said lifting valve, and by virtue of the fact that, in each case, the contour of only one cam acts on the lifting profile. For the switch to another lifting profile, a switch is made to the contour of another cam. Such valve control is already known from DE 42 30 877 A1. Here, a camshaft block with two different cam contours is arranged rotationally conjointly but axially displaceably on a camshaft. In accordance with the axial position of the cam block, a cam contour is operatively connected to the lifting valve via an intermediate element (transmission lever). The axial displacement of the cam block for the purposes of varying the valve parameters is performed, during the base circle phase, by way of a thrust ring counter to the action of a restoring spring.
DE 195 19 048 A1 has already disclosed a variable valve drive for an internal combustion engine, in which it is likewise the case that two cams which are of different design in terms of their cam contour are arranged directly adjacent to one another on the camshaft. The change of the cam engagement is realized by way of an axial displacement of the camshaft with the cams situated thereon.
Furthermore, DE 195 20 117 C2 has already disclosed a valve drive of an internal combustion engine, in the case of which an axially displaceable cam block with at least two different cam tracks is arranged rotationally conjointly on the camshaft. The adjustment of the cam block is realized by way of an adjustment member which is guided in the interior of the camshaft. By way of a double-acting hydraulic or pneumatic piston-cylinder unit arranged at the face side on the camshaft, the adjustment member is displaced in the interior of the camshaft. The adjustment member is connected to a driver piece which extends through an elongated hole arranged in the camshaft and which issues into a bore of the cam block.
A disadvantage of the cited prior art is that different opening and closing times and different valve opening lifts cannot be set in continuously variable fashion. A further disadvantage is that, with said known approaches, it is not possible for an existing valve drive without variability to be converted to a valve drive with variability without the need for changes to be made to peripheral components aside from those directly required for realizing the variability.